/*
 * Copyright (c) 2015 Cisco Systems, Inc. and others.  All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.mdsal.binding.api;

import java.util.List;
import org.eclipse.jdt.annotation.NonNull;
import org.opendaylight.yangtools.yang.binding.DataObject;

/**
 * Interface implemented by classes interested in receiving notifications about changes to a data tree. It provides
 * a cursor-based view of the change, which has potentially lower overhead and allow more flexible consumption of change
 * events.
 */
public interface DataTreeChangeListener<T extends DataObject> {
    /**
     * Invoked when there was data change for the supplied path, which was used to register this listener.
     *
     * <p>
     * This method may be also invoked during registration of the listener if there is any pre-existing data in the
     * conceptual data tree for supplied path. This initial event will contain all pre-existing data as created.
     *
     * <p>
     * Note: If there is no pre-existing data, the method {@link #onInitialData} will be invoked.
     *
     * <p>
     * A data change event may be triggered spuriously, e.g. such that data before and after compare as equal.
     * Implementations of this interface are expected to recover from such events. Event producers are expected to exert
     * reasonable effort to suppress such events.
     *
     *<p>
     * In other words, it is completely acceptable to observe a {@link DataObjectModification}, while the state observed
     * before and after- data items compare as equal.
     *
     * @param changes List of change events, may not be null or empty.
     */
    void onDataTreeChanged(@NonNull List<DataTreeModification<T>> changes);

    /**
     * Invoked only once during registration of the listener if there was no data in the conceptual data tree for the
     * supplied path, which was used to register this listener, and after this {@link #onDataTreeChanged(List)} would
     * always be invoked for data changes.
     *
     * <p>
     * Default implementation does nothing and is appropriate for users who do not care about ascertaining initial
     * state.
     */
    // FIXME: 14.0.0: this method should be non-default
    default void onInitialData() {
        //no-op
    }
}